Ch 43 Body’s Defenses AP Biology

Vertebrate Nonspecific Defense Barriers, Phagocytes, Proteins, Complement System, & Inflammation 1. Barriers [Skin] Prevents entry of pathogens (intact epidermis, hairs to filter, etc.) Secrete acids (inhibit growth of microorganisms, destroy bacteria in food), mucous (wash away & trap), & chemicals (lysozyme to destroy cell walls)

2. Phagocytes Lysosomes within cells fuse with pathogens & release hydrolytic enzymes Neutrophils (phagocytosis of pathogens) [W.B.C.] Monocytes (phagocytize pathogens) some are wandering (throughout interstitial fluid & lymph) others are fixed (found in lymph nodes) Eosinophils Killer cells (kill infected cells)

3. Proteins Interferons (interfere with viral reproduction) Secreted by infected cells, stimulate neighboring cells to produce antiviral proteins to inhibit growth of virus. Active only against viruses. Recombinant DNA technology used to make synthetic forms in hope of slowing cancer growth.

4. Complement System Attract phagocytes [found in plasma] Triggered by antibodies to antigen

5. Inflammation Cells release histamine causing dilation of vessels. Increase blood supply due to dilation causes redness and warmth. Swelling (edema) of affected area caused by fluid loss from vessels. Vessels become more permeable/leaky (caused by histamine) Increased blood flow brings larger numbers of phagocytes to infected area. Fever – widespread inflammatory response. Pyrogens (released by W.B.C.s) reset thermostat in hypothalamus. Fever interferes with viral activity.

Vertebrate Specific Disease Specificity Diversity Self/non-self recognition Memory

Specificity Response is not random. Recognition and elimination of particular microorganism and pathogen. Body responds to antigen (substance that initiates response [capsule, cell wall, toxin]; unique molecular shaped conferred by surface proteins) by releasing antibody (protein produced by B-cells that bind to antigens)

Diversity Antibody amino acid sequence on variable region constantly modified.

Self/Non-self Recognition Blood groups, tissue grafts and organ transplants, autoimmune disorders. Major histocompatibility complex (MHC). Proteins embedded in plasma membranes.

Memory Memory cells survive in system for long period of time. Activated during secondary immune response.

3 steps to Immune Response Recognition of Invader [Caught on Radar] Activation of System [Man your Battle Stations!] Response to Invader [Fire all weapons!!]

Active Immunity Individual is infected and forms a defense against pathogen by mounting either a humoral response (antibody formation) or a cell-mediated response (lymphocytes) Vaccinations (weakened forms of pathogen or toxin) stimulate antibody production and formation of memory cells without causing the disease. Vaccines are made from killed pathogens or weakened strains that cause antibody production but not the disease.

Passive Immunity Transferred from one individual to another (mother to baby). Antibodies are transferred in colostrum of nursing moms. Antibodies can be give to adults as well. Temporary jump start to immunity. Work long enough to prevent infection.

Rule Once the immune system has been activated (actively or passively) the response can be the formation of antibodies (humoral) or lymphocytes (cell-meidated).

Humoral Response Antibodies are Y shaped protein molecules composed of two identical long polypeptides and two identical short polypeptides. Function of antibodies include: Recognition and binding to antigen Inactivation of the antigen

Humoral Response cont. Regulated by B-cells. (B-cells form & develop from stem cells in marrow) -Concentrated in lymph nodes, spleen. (Spleen is largest lymphatic structure. It is responsible for the production of B-cells, phagocytizes bacteria and worn out/damaged R.B.C.s, stores and releases blood in case of demand (i.e. hemorrhage) Have antigen receptors on membrane to recognize specific pathogen. Can only bind to one type of antigen.

Humoral Repsonse cont. Plasma Cells Secrete antibodies specific for antigen (approx. 2000 molecules/sec.) B-memory cells are also formed to provide immunological memory (life for months or years). During secondary response, react much more quickly and aggresively.

Cell-mediated Response Lymphocytes respond to antigen. Work together w/ macrophages that have engulfed pathogen. Surface of macrophage has signals (self v. non-self) that are recognized by lymphocytes. T lymphocytes (T-cells) form from pluripotent stem cells, develop in thymus.

Cell-mediated Response cont. Cells only activated by cells previously infected with an antigen (Cell-to-Cell combat) Cannot recognize free floating antigens in body fluids (unlike antibodies). Once activated, T-cells become specialized forms called helper T (TH) or killer/cytotoxic T (TC)

Cell-mediated Response cont.